Unable to Fix the Formula

Example:
A: 90,500 (Inclusive Fee 5%)
B: 4,525 (Fee)
C: 85,975

Rules:

1. The B is a fixed percentage of 5%

2. I will only have the C at all time.

3. The B is a actually come from A* fixed rate 5% (Ex: 90,500*5%)

4. The A is a total of C+B=A.

So, question is, how do I get this A*B% if I only have C at all time.

Need all expert help to guide me in solving this formula. Appreciate it if any expert can show. Thanks.